1. Field of the Invention
The present invention relates to a process for manufacturing buried hetero-structure (BH) laser diodes (LD).
2. Description, of the Related Art
Patent Literature 1 (US Application Publication No. 2008/0219312) discloses a quantum cascade laser (QCL) device having a buried hetero-structure. The quantum cascade laser device described in the patent literature 1 has a stripe-shaped mesa structure extending along a predetermined direction of a principal surface of a substrate. Further; the cross-section of the mesa structure in a direction perpendicular to the predetermined direction has a rectangle shape or an inverted mesa shape. With such a configuration, the quantum cascade laser device has high slope efficiency and operates with a stable single transverse mode.
In general, a process for the manufacturing of a buried hetero-structure laser diode (BH LD) includes a step of growing a stacked semiconductor layer including an active layer onto a semiconductor substrate and a step of forming a semiconductor mesa. In addition, the step of the semiconductor mesa includes the steps of forming a stripe-shaped mask extending in a predetermined direction on the stacked semiconductor layer and etching the stacked semiconductor layer through the mask. The mask is made of, for example, SiN or SiO2. Such a production process further includes a step of forming a buried layer on a side surface of the semiconductor mesa while using the mask as a selective growth mask and a step of forming an upper electrode on the semiconductor mesa and forming a lower electrode on the back surface of the semiconductor substrate.